A study led by Massachusetts General Hospital (MGH) investigators identifies two subanesthetic dosage levels of the anesthetic drug ketamine that appear to provide significant symptom relief to patients with treatment-resistant depression. In the October 2018 issue of Molecular Psychiatry they describe finding that single intravenous doses of 0.5 mg/kg and 1.0 mg/kg were more effective than an active placebo in reducing depression symptoms over a three-day period. Two lower dosage levels that were tested did not provide significant symptom relief, although some improvement was noted with the lowest 0.1 mg/kg dose. (Source)